Voltage reference devices



July 29, 1958 H. w; COLLINS 2,845,590

VOLTAGE REFERENCE DEVICES Filed April 18, 1955 Fig.2.

WITNESS ES.

Loud

INVENTOR H urd ollins.

2,845,590 Patented July 29, 1958 VOLTAGE REFERENCE DEVICES Howard W. Collins, Pittsburgh, Pa., assignor to Westing house Electric Corporation, East Pittsburgh, Pa, a con poration of Pennsylvania Application April 18, 1955, Serial No. 502,101

8 Claims. (Cl. 321-16) This invention relates to voltage reference devices and more particularly to means for temperature compensating these reference devices.

The saturation voltage of a square loop magnetic core is commonly used to provide a static reference device for use in electrical systems. That is, the average output voltage of the reference device remains substantially constant for a wide range of change in the magnitude of the input voltage provided the input voltage is of sufficient magnitude to effect a substantially complete saturation of the square loop magnetic core. However, a problem results in applying the reference device because the saturation flux density of square loop magnetic materials varies with changes in the temperature of the surrounding air. Any accurate saturating reference device which must operate over a temperature range must therefore have some means of temperature compensation.

Heretofore, reference devices have been temperature compensated by means of negative temperature coefficient resistors in series with the output, positive coefiicient resistors shunting the output, or a combination of both. The compensating resistors maintain a constant current output even though the saturation voltage of the magnetic core changes with temperature. Unfortunately, the reference device is only compensated for one particular output current level and the reference device is altered from a constant voltage source to essentially a constant current source. Further, accuracy is difli'cult to achieve over a wide temperature range. In addition, the output power is decreased by the power absorbed in the compensating resistors and the maximum power output of such a prior art reference device is limited by the amount of power dissipation which can be tolerated in commercially available non-linear resistors. It is also to be noted that a reference device which uses a shunt compensating resistor often has an undesirably low output impedance.

An object of this invention is to provide for temperature compensating a voltage reference device over a wide range of output current load values and over a wide temperature range.

Another object of this invention is to provide for increasing the efliciency of a temperature compensated voltage reference device and provide for obtaining a high current output therefrom.

A further object of this invention is to so temperature compensate a voltage reference device that the reference device remains a voltage reference.

A still further object of this invention is to provide a temperature compensated voltage reference device which acts as a high source impedance when supplying energy to a load.

A specific object of this invention is to provide for so interconnecting a winding of a compensating saturable magnetic device with the secondary winding of a saturating transformer, whose magnetic core member has a much lower temperature coefficient of saturation flux density than the magnetic core member of the compensating saturable magnetic device, that the resultant output voltage remains substantially constant with changes in temperature over a wide range.

Other objects of this invention will become apparent from the following description when taken in conjunction with the accompanying drawing, in which:

Figure l is a schematic diagram of an embodiment of this invention in which the primary windings of the main and compensating saturating transformer are connected in parallel circuit relationship with one another;

Fig. 2 is a schematic diagram of circuits and apparatus illustrating another embodiment of this invention in which the primary windings of the main and compensating saturating transformer are connected in series circuit relationship with one another; and

Fig. 3 is a schematic diagram of apparatus .and circuits illustrating still another embodiment of the invntion in which the compensating saturable magnetic device includes a magnetic core member and a single reactor winding disposed in inductive relationship therewith.

Referring to Fig. 1 there is illustrated a voltage reference device 10 for maintaining a substantially constant :direct-currentvoltage across a load 12 over a wide range of change in the temperature of the air surrounding the voltage reference device Eli} and over a wide range of change in the magnitude of the alternating-current input voltage applied to input terminals 14 and 14' and over a wide range of output load currents. In general, the voltage reference device 10 comprises a main saturating transformer 16 and a compensating saturable magnetic device, specifically a compensating saturating transformer 18,which cooperates with the main saturating transformer .16 to temperature compensate the voltage reference device 10 over a wide range of temperature change in the air surrounding the device 10.

The main saturating transformer 16 comprises a magnetic core member 20, preferably formed from square loop core material. In order to magnetically saturate the magnetic core member 20 in accordance with the input Voltage, as applied to the input terminals 14 and .14, a primary winding 22 is disposed in inductive relationship withthe magnetic core member 20. As shown, the primary winding 22 is connected in series circuit relationship with a current limiting resistor 24, the series circuit being electrically connected across the input terminals 14 and 14. In operation, the alternatingmurrent voltage applied to the input terminals 14 and 14' is always 'of sufiicient magnitude to efiect a substantially complete magnetic saturation of the magnetic core member 20.

When the voltage across the input terminals 14 and 14' is of such magnitude as to effect a substantially complete magnetic saturation of the magnetic core member 20, the impedance of the primary winding 22 is extremely low. Therefore, the current limiting resistor 24 is connected in series circuit relationship with the primary winding 22 in order to limit the magnitude of the current flow through the primary winding 22 when the mag netic core member 20 is saturated and thus prevent excessive heating and resultant damage to the primary winding 22.

In order to produce an average output voltage from the saturating transformer 16, which is substantially independent of the magnitude of the input voltage across the input terminals 14 and 14', a secondary winding 26 is disposed in inductive relationship with the magnetic core her 20. This can be better understood by considering that it takes a predetermined number of volt seconds to saturate the magnetic core member 20, and if the input voltage across the terminals 14 and 14 increases, the magnetic core member 20 will saturate within a predetermined time interval which will be a shorter duration than in the case when the input voltage is of lesser magnitude. Further, the areas under the voltage-time curves for the primary winding 22 are of substantially equal magnitude irrespective of the magnitude. of the voltage across the input terminals 14 and 14', since the same predetermined volt seconds are required to saturate the magnetic core member 20 each time. Therefore, since there is always a substantially complete magnetic saturation of the magnetic core member 20 for all magnitudes of voltage across the input terminals 14 and 14' above a predetermined value, the average voltage across the secondary winding 26 remains substantially constant for varying magnitudes of voltage across the input terminals 14 and 14'.

As illustrated, the compensating saturating transformer 18 comprises a magnetic core member 28 and a primary winding 30 and a secondary winding 32 disposed in inductive relationship with the magnetic core member 28. In order to render the primary winding 30 of the compensating saturating transformer 18 responsive to the input voltage across the terminals 14 and 14', the primary winding 30 is connected in series circuit relationship with a current-limiting resistor 34 and the series circuit is electrically connected to the input terminals 14 and 14. Thus, as can be seen from Fig. 1, the primary windings 22 and 30 are connected in parallel circuit relationship with one another, the parallel circuit being responsive to the input voltage applied to the terminals 14 and 14.

In operation, the current-limiting resistor 34 functions to limit the current flow through the primary winding 30 when the magnetic core member 28 is saturated. Of course, in operation, the voltage across the terminals 14 and 14 must always be of such magnitude as to effect a substantially complete saturation of the magnetic core member 28 of the compensating saturating transformer 18.

In practice, the magnetic core member 28 of the compensating saturating transformer 18 is constructed of a magnetic material that has a much greater temperature coefficient of saturation flux density than does the magnetic material from which the magnetic core member of the main saturating transformer 16 is constructed. Temperature coeflicient of saturation flux density is defined herein as the percentage change of flux density per degree temperature change. Also, in practice, the saturation voltage E appearing across the secondary winding 32 of the compensating saturating transformer 18 is selected so that the ratio of E to E (the saturation voltage appearing across the secondary winding 26 of the main saturating transformer 16) is in inverse proportion to the temperature coefiicients of saturation flux density of the magnetic core materials of the magnetic core members 20 and 28 of the voltage reference device 10. When using a core material such as ferrite for the magnetic core member 28, E may be made approximately one-sixth the value of E The secondary windings 26 and 32 are so disposed and interconnected that the saturation voltages E and E oppose each other and the net output voltage E is the difference between E and E As the temperature varies, E varies a given percent as determined by the temperature coefiicient of saturation flux density of the magnetic core member 20. On the other hand, E varies by a greater percentage as determined by the relatively greater temperature coefiicient of saturation flux density of the magnetic core member 28. Since the values of the saturation voltages E and E are selected in inverse proportion to the temperature coefficients of saturation flux density, the absolute value of the variations of E and B are the ,4 same but of opposite polarities. Therefore, these variations cancel each other and the net output voltages E remains constant over a wide range of change of the temperature of the air surrounding the voltage reference device 10. Of course, the reason the magnetic core member 28 of the compensating saturating transformer 18 is constructed of a magnetic material having a much greater temperature coeflicient of saturation flux density than the material from which the magnetic core-member 20 is constructed, is so that the voltage E can be made small as compared to the voltage E thus making the net output voltage E relatively large.

In order to rectify the net output voltage E a fullwave, dry-type rectifier 36, having input and output terminals, is provided. In particular, the secondary windings 26 and 32 are connected in series circuit relationship with one another, the series circuit being connected to the input terminals of the rectifier 36. As illustrated, the output terminals of the rectifier 36 are connected to the load 12. Thus, a voltage is produced across the load 12 which is proportional to the difference between the saturation voltages E and E Of course, the rectifier 36 may be omitted if an alternating-current output is desired.

In the operation of the apparatus shown in Fig. l, the magnetic core members 20 and 28 are both driven to positive saturation during one-half cycle of operation and then are driven to negative saturation during the next half-cycle of operation. However, it is to be noted that after the magnetic core member 28 of the compensating saturating transformer 18 saturates, current continues to flow through its primary winding 30 until the end of each half-cycle of operation, thus holding the magnetic core member 28 in saturation throughout each half-cycle.

In practice, the current-limiting resistors 24 and 34 can be replaced by suitable linear inductance members (not shown) and when such replacements are made the power dissipation in the primary circuit of the voltage reference device 10 is minimized.

Referring to Figure 2, there is illustrated another embodiment of this invention in which like components of Figs. 1 and 2 have been given the same reference characters. The main distinction between the apparatus illustrated in Figs. 1 and 2 is that in the apparatus of Fig. 2 the primary winding 22 and a primary winding 38, corresponding to the primary winding 30 of Fig. 1, are connected in series circuit relationship with one another, the series circuit being connected to the input terminals 14 and 14. In the apparatus of Fig. 1, the primary windings 22 and 30 are connected in parallel circuit relationship with one another, the parallel circuit being connected to the input terminals 14 and 14'. It is also to be noted that the primary winding 38 of the compensating saturating transformer 40 of Fig. 2 is wound oppositely from the primary winding 30 of the compensating saturating transformer 18 as illustrated in Fig. l.

.The operation of the apparatus illustrated in Fig. 2 is similar to the operation of the apparatus illustrated in Fig. 1. However, the apparatus in Fig. 2 should be so constructed that the magnetic core member 28 of the compensating saturating transformer 40 saturates, during each half-cycle of operation, before the magnetic core member 20 of the main saturating transformer 16 saturates. If the magnetic core member 20 were to saturate before the magnetic core member 28, then the output from the compensating saturating transformer 40 would cause the net output voltage E to instantaneously reverse its polarity once the magnetic core member 20 saturates.

Referring to Fig. 3, there is illustrated still another embodiment of this invention. The main distinction between the apparatus illustrated in Figs. 2 and 3 is that in the apparatus illustrated in Fig. 3 the compensating saturable magnetic device comprises a compensating saturable reactor 42 having a magnetic core member 44 and a single reactor winding 46 disposed in inductive relationship with the magnetic core member 44. In practice, the magnetic core member 44 is constructed of a magnetic material having a much greater temperature coefiicient of saturation flux density than the material from which the magnetic core member 20, illustrated in Fig. 3, is constructed. The reason for this is the same as that reason given with respect to the apparatus of Fig. 1. I

The secondary Winding 26 of the saturating transformer 16 and the reactor winding 46 of the compensating saturable reactor 42 are so disposed and interconnected that the net output voltage E is proportional to the difference in the saturation voltages E and E In particular, the secondary winding 26 and the reactor winding 46 are connected in series circuit relationship with one another, the series circuit being connected to the input terminals of the rectifier 36. Thus, a voltage is produced across the load 12 as shown in Fig. 3 which is proportional to the difference in the voltages appearing across the secondary winding 26 and the reactor winding 46.

In operation the magnitude of the voltage applied to the terminals 14 and 14', as illustrated in Fig. 3, is always sufiicient to effect a substantially complete magnetic saturation of the magnetic core members 20 and 44 during each half-cycle of operation. In particular, during one half-cycle of operation the magnetic core member 26' of the saturating transformer 16 is driven from negative to positive saturation.- During this same half-cycle of operation the magnetic core member 44 must first be driven to saturation before the magnetic core member 20 saturates. However, once the magnetic core member 20 saturates, the current flow through the reactor winding 46 decreases to zero magnitude and the magnetic core member 44 snaps back from positive saturation to its remnant flux density. This sudden flux change induces a voltage spike across the magnetic core member 44, but this spike coincides with the saturation of the magnetic core member 20 and is not distinguishable in the net output voltage E During the next half-cycle of operation the magnetic core member 20 is driven from positive to negative saturation. During this same half-cycle of operation the magnetic core member 44 is driven from its remnant flux density to negative saturation before the magnetic core member 29 is driven to negative saturation. Thus, the output current of the saturating transformer 16 is used during each half-cycle of operation to effect a saturation of the magnetic core member 44 of the compensating saturable reactor 42.

The temperature compensated voltage reference de vices shown in Figs. 1-3 have several advantages over resistive compensation methods. For instance, the amount of compensation is essentially independent of the output current level, whereas resistive techniques are set for only one particular value of output current. If frequency compensation is not necessary, this makes possible the manufacture of a standard reference which will be compensated over a wide range of output current values. In addition, resistive compensation alters the reference from a true reference voltage to a current reference, while temperature compensation with a saturable device retains the inherent voltage reference characteristics of a saturable core. In the apparatus of this invention, the maximum practical output current is not limited by the internal heating which can be tolerated in a series negative tem perature coefiicient resistor, and the usable output current is not decreased in the apparatus of this invention by the amount which must pass through a shunt resistor.

The accuracy of the apparatus shown in Figs. 1 through 3 is as great as that obtainable with resistive compensation. Further, a reference compensated with a saturable reactor device as shown in Figs. 1 through 3 hasa high output impedance. In contrast, a prior art reference with a shunt resistor across its output presents a low impedance to the load, and it is often necessary to use an additional series choke in these prior art devices to provide a high impedance when supplying loads such as the bias windings of a magnetic amplifier.

Since numerous changes may be made in the above apparatus and circuits, and different embodiments of the invention may be made without departing from the spirit and scope thereof, it is intended that all matter contained in the foregoing description or shown in the accompanying drawing shall be interprteted as illustrative and not in a limiting'sense.

I claim as my invention:

1. In a temperature compensated voltage reference device responsive to an input voltage for supplying energy to a load, the combination comprising, a. saturating transformer having a magnetic core member and a primary winding and a secondary winding disposed in inductive relationship with the magnetic core member, circuit means for rendering the primary winding responsive to the input voltage, a compensating saturable magnetic device including another magnetic core member and a winding disposed in inductive relationship with said another magnetic core member, the input voltage always being of sufilcient magnitude to effect a substantially complete magnetic saturation of the magnetic core member of the saturating transformer and of the said another magnetic core member, and the said another magnetic core member having a substantially greater temperature coefficient of saturation flux density than the magnetic core member of the saturating transformer, and other circuit means for so interconnecting said secondary winding and the winding of the compensating saturable magnetic device with one another and with said load that the voltage produced across the said load is proportional to the difference in the voltage existing across the said secondary winding and the winding of the compensating saturable magnetic device.

2. In a temperature compensated voltage reference device responsive to an input voltage for supplying energy to a load, the combination comprising, a main saturating transformer having a magnetic core member and a primary winding and a secondary winding disposed in inductive relationship with the magnetic core member, a compensating saturating transformer including a magnetic core member and a primary winding and a secondary winding disposed in inductive relationship with the magnetic core member of the compensating saturating transformer, circuit means for rendering the primary windings of the main and compensating saturating transformer responsive to the input voltage, the input voltage always being of sufficient magnitude to effect a substantially complete magnetic saturation of the magnetic core members of the main and compensating saturating transformer, and the magnetic core member of the compensating saturating transformer having a substantially greater temperature coefficient of saturation flux density than the magnetic core member of the main saturating transformer, and other circuit means for so interconnecting the secondary windings of the main and compensating saturating transformer with one another and with said load that the voltage produced across the load is proportional to the difference in the voltages existing across said secondary windings.

3. In a temperature compensated voltage reference device responsive to an input voltage for supplying energy to a load, the combination comprising, a main saturating transformer having a magnetic core member and a primary winding and a secondary winding disposed in inductive relationship with the magnetic core member, a compensating saturating transformer including a magnetic core member and a primary winding and a secondary winding disposed in inductive relationship with the magnetic core member of the compensating saturating transformer, circuit means for connecting the primary windings of the main and compensating saturating transformer in parallel circuit relationship with one another and for rendering the parallel circuit responsive to the input voltage, the input voltage always being of sufiicient magnitude to effect a substantially complete magnetic saturation of the magnetic core members of the main and compensating saturating transformer, and the magnetic core member of the compensating saturating transformer having a substantially greater temperature coefficient of saturation flux density than the magnetic core member of the main saturating transformer, and other circuit means for so interconnecting the secondary windings of the main and compensating saturating transformer with one another and with said load that the voltage produced across the load is proportional to the difference in the voltages existing across said secondary windings.

4. In a temperature compensated voltage reference device responsive to an input voltage for supplying energy to a load, the combination comprising, a main saturating transformer having a magnetic core member and a primary winding and a secondary winding disposed in inductive relationship with the magnetic core member, a compensating saturating transformer including a magnetic core member and a primary and a secondary winding disposed in inductive relationship with the magnetic core member of the compensating saturating transformer, circuit means for connecting the primary windings of the main and compensating saturating transformer in series circuit relationship with one another and for rendering the series circuit responsive to the input voltage, the input voltage always being of sufficient magnitude to effect a substantially complete magnetic saturation of the magnetic core members of the main and compensating saturating transformer, and the magnetic core member of the compensating saturating transformer having a substantially greater temperature coefiicient of saturation flux density than the magnetic core member of the main saturating transformer, and other circuit means for so interconnecting the secondary windings of the main and compensating saturating transformer with one another and with said load that the voltage produced across the load is proportional to the difference in the voltages existing across said secondary windings.

5. In a temperature compensated voltage reference device responsive to an input voltage for supplying energy to a load, the combination comprising, a saturating transformer having a magnetic core member and a primary winding and a secondary winding disposed in inductive relationship with the magnetic core member, circuit means for rendering the primary Winding responsive to the input voltage, a compensating saturable reactor including a magnetic core member and a reactor winding disposed in inductive relationship with the magnetic core member of the compensating saturable reactor, other circuit means for so interconnecting said reactor winding and the secondary winding of the saturating transformer with one another and with said load that the voltage produced across the load is proportional to the difference in the voltages existing across said secondary winding and across the said reactor winding, said input voltage always being of sufficient magnitude to effect a substantially complete magnetic saturation of the magnetic core members of the saturating transformer and the compensating saturable reactor, and the magnetic core member of the compensating saturable reactor having a substantially greater coefiicient of saturation flux density than the magnetic core member of the saturating transformer.

6. In a temperature compensated voltage reference device responsive to an input voltage for supplying energy to a load, the combination comprising, a main saturating transformer having a magnetic core member and a primary winding and a secondary winding disposed in inductive relationship with the magnetic core member,

a compensating saturating transformer including a magnetic core member and a primary winding and a secondary winding disposed in inductive relationship with the magnetic core member of the compensating saturating transformer, circuit means for connecting the primary windings of the main and compensating saturating transformer in parallel circuit relationship with one another and for rendering the parallel .circuit responsive to the input voltage, the input voltage always being of sufiicient magnitude to effect a substantially complete magnetic saturation of the magnetic core members of the main and compensating saturating transformer and the magnetic core member of the compensating saturating transformer having a substantially greater temperature coeflicient of saturation flux density than the magnetic core member of the main saturating transformer, a rectifier having an input and an output, the output of the rectifier being for connection to said load, and further circuit means for connecting the secondary windings of the main and compensating saturating transformer in series circuit relationship with one another and for connecting the series circuit to the input of the rectifier so that a voltage proportional to the difference in the voltages existing across the said secondary windings is applied to the input of the rectifier.

7. In a temperature compensated voltage reference device responsive to an input voltage for supplying energy to a load, the combination comprising, a main saturating transformer having a magnetic core member and a primary winding and a secondary winding disposed in inductive relationship with the magnetic core member, a compensating saturating transformer including a magnetic core member and a primary and a secondary wind ing disposed in inductive relationship with the magnetic core member of the compensating saturating transformer, circuit means for connecting the primary windings of the main and compensating saturating transformer in series circuit relationship with one another and for rendering the series circuit responsive to the input voltage, the input voltage always being of sufficient magnitude to effect a substantially complete magnetic saturation of the magnetic core members of the main and compensating saturating transformer, and the magnetic core member of the compensating saturating transformer having a ubstantially greater temperature coefficient of saturation flux density than the magnetic core member of the main saturating transformer, a rectifier having an input and an output, the output of the rectifier being for connection to said load, and further circuit means for connecting the secondary windings of the main and compensating saturating transformer in series circuit relationship with one another and for connecting the series circuit including said secondary windings to the input of the rectifier so that a voltage is applied to the input of the rectifier proportional to the difference in the voltages existing across the said secondary windings.

8. In a temperature compensated voltage reference device responsive to an input voltage for supplying energy to a load, the combination comprising, a saturating transformer having a magnetic core member and a primary winding and a secondary winding disposed in inductive relationship with the magnetic core member, circuit means for rendering the primary winding responsive to the input voltage, a compensating saturable reactor including a magnetic core member and a reactor winding disposed in inductive relationship with the magnetic core member of the compensating saturable reactor, a rectifier having an input and an output, the output of the rectifier being for connection to said load, and further circuit means for connecting the secondary winding of the saturating transformer and the reactor winding of the compensating saturable reactor in series circuit relationship with one auother and for connecting the series circuit to the input of the rectifier so that a voltage is applied to the inf of the rectifier proportionalto the dif- 9 10 ference in the voltages existing across the secondary wind ing a substantially greater coefiicient of saturation flux ing of the saturating transformer and across the reactor density than the magnetic core member of the saturatwinding of the compensating saturable reactor, said ining transformer. put voltage always being of sufiicient magnitude to effect a substantially complete magnetic saturation of the mag- 5 References Cited in the file of this Patent netic core members of the saturating transformer and UNITED STATES PATENTS the compensating saturable reactor and the magnetic core member of the compensating saiturable reactor hav- 9 Rleber July 1924 

